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problem. At very low temperatures, the simulation would get stuck in a temporary state and wouldn't
settle into the true equilibrium state. My key insight—my
ansatz
—was in recognizing that the fact that
the material was organizing itself into parallel, variably spaced, linear chains of copper and oxygen
atoms was telling us something fundamental about the symmetry of YBCO at very low temperatures.
The material was behaving not as a two-dimensional planar system, but as a much simpler one-
dimensional linear system. Unlike the two-dimensional problem, the one-dimensional problem had an
analytical solution; we could solve it with paper and pencil, allowing us to fully map YBCO's phase
superconductivity of the material. Nonetheless, I had once again found a satisfying trick to solve
another challenging scientific puzzle, and that's all that mattered to me at the time.
After graduating from UC Berkeley, I went off to Yale University in fall 1989 to pursue a Ph.D.
in physics. I was planning to study theoretical condensed matter physics—the theory behind the
behavior of solids and liquids. After two years, I'd completed my coursework and passed my exams,
and it was time to select a Ph.D. topic and adviser. Funding was tight, however, and, like other
graduate students in physics, I was being steered toward increasingly applied areas of research—in
my case, the study of semiconductor devices. This wasn't quite the “big-picture” science I'd had in
mind when I decided to go into physics in the first place. I was somewhat disillusioned and felt as if
I'd lost my bearings. Facing a vocational crisis, I opened up the university catalog one day to see
what other scientific research was being done at Yale where I might be able to apply my math and
physics interests to working on a big-picture problem of significance.
As I scrolled through the catalog, I discovered that a professor in the Department of Geology and
Geophysics, Barry Saltzman, was using the tools of physics to simulate Earth's climate. That sounded
like a big-picture problem to me, and an important one at that. I scheduled an appointment to meet
with Saltzman that week. As I talked with him, I became even more excited about the possibility of
doing research in this area. He gave me a few articles to read and told me to get back to him if this
subject matter seemed to be my cup of tea. I scoured the papers over the weekend. While the
terminology and mathematical conventions were a bit different from those I'd encountered in my
physics training, I got the gist of the articles—much as someone who speaks Spanish can roughly
understand a person speaking Portuguese. On Monday, I told Barry that I was indeed interested in
pursuing research in this area. He had some additional funding and could support me on a trial basis
for the summer. If all worked out, I could stay on with him to do my Ph.D.
That summer, I assisted a postdoctoral researcher of Barry's with a project aimed at simulating
the climate of the Cretaceous period with a state-of-the-art computer model. The Cretaceous period
ended about 65 million years ago—with a bang, in fact. That's when the dinosaurs went extinct, due
to—it is now generally accepted—the impact of a large asteroid that struck Earth, sending massive
amounts of dust into the atmosphere, blocking out much of the incoming sunlight, and sending Earth—
in essence—into a quasi-perpetual years-long winter. What we were interested in, however, was the
period of peak Cretaceous warmth roughly 35 million years earlier. We were trying to figure out how
the high-latitude continents could have been as warm as they were. Fossil evidence indicates that
dinosaurs back then were wandering Antarctica! Geological evidence suggests that greenhouse gas
concentrations were higher than modern levels by perhaps a factor of four or more—enough to
account for the overall extent of apparent global warmth at the time. What the models could not
explain, however, was the paleodata indicating that the tropics warmed up only a little, while the
